Conventional vapor-compression air conditioning systems use a working fluid such as chlorofluorocarbons (CFCs), e.g., FREON. A liquid CFC is typically introduced into a low-pressure heat exchanger where it absorbs heat at a low temperature and vaporizes. A compressor re-pressurizes the vapors that are then introduced to a high-pressure heat exchanger where heat is rejected to the environment and the vapors condense. The condensate is reintroduced into the low-pressure heat exchanger to complete the cycle.
The use of CFCs raises two important environmental concerns. First, CFCs are stable until they reach the stratosphere where they decompose into chlorine free radicals that catalyze the destruction of ozone. Second, CFCs absorption of infrared radiation contributes to global warming. Therefore, CFCs cannot be released into the environment and must be contained within the air conditioning system. Unfortunately, leaks are not uncommon in air conditioning systems. With the prevalence of CFC-based air conditioning systems in our world, there is a great need to provide non-CFC-based air conditioning systems.
The use of low pressure air in place of CFCs as the air conditioning working fluid has been considered. However, proposed systems have heat problems within the expansion area and frosting problems in the suction area. In some arid regions of the United States, an air-based air conditioner known as a “swamp cooler” has been used with some success. However, its usefulness is limited to very dry climates. Further, the cooled air produced by a swamp cooler is very humid thereby making the cooled air feel “clammy”.